An ergodic Markov chain is started in equilibrium (i.e., with initial probability vector w). The mean time until the next occurrence of state si is \bar{m}_i= \sum\limits_{k} w_k m_{ki}+ w_i r _i. Show that \bar{m}_i= zii/wi, by using the facts that wZ = w and mki =(zii − zki)/wi.